The present invention relates to a hexamethyldisilazane (HMDS) supplying apparatus. More particularly, the invention relates to an HMDS supplying apparatus that senses the flow of HMDS through a flowmeter and controls the amount which is flowing.
In a semiconductor fabricating process, a photosensitive layer is formed as a pattern on a semiconductor substrate prior to additional steps in the formation of a semiconductor device. If adhesion of the photosensitive layer is weak, the layer may become separated from the semiconductor substrate during a subsequent etching step. As a result, an undesired portion of the substrate may be etched in the etching step and result in an inferior quality semiconductor device. Thus, it is very important to improve adhesion of the photosensitive layer in semiconductor fabrication. Also, an important processing parameter in the photosensitive layer deposition process is the affinity between the photosensitive layer and the surface of a wafer, since this has an effect on the pattern being formed.
Since the photosensitive layer is hydrophobic and the surface of wafer is hydrophilic, the natural affinity between the photosensitive layer and the wafer surface is not good. Thus, for the purpose of improving the affinity, an HMDS-treatment step is utilized wherein the affinity-improving agent HMDS is sprayed on the wafer surface in a vapor state.
In such a case, if HMDS is not evenly sprayed on the wafer to provide a uniform coating, the photosensitive layer may become separated from a portion of the wafer which has a weak affinity between the photosensitive layer and the wafer surface. On the other hand, if the affinity is too strong, a portion which should be removed by a developing process may in fact remain.
Generally, in order to improve the adhesion between the photosensitive layer and the wafer surface, a process of depositing HMDS on the wafer surface is performed using an HMDS supplying apparatus before depositing the photosensitive layer. For such processes, the HMDS supplying apparatus is usually installed in the photosensitive depositing apparatus.
Hereinafter, the conventional HMDS supplying process using a photosensitive layer depositing apparatus will be described in greater detail.
FIG. 1 is a structural diagram showing a conventional HMDS supplying apparatus installed in a photosensitive layer depositing apparatus.
Specifically, a container 1 for containing HMDS, which is a liquid at room temperature, is connected to a gaseous nitrogen supplying portion 3 serving as a means to supply gaseous nitrogen as a carrier gas for carrying liquid HMDS stored in the container 1. HMDS is carried from the container 1 together with gaseous nitrogen and is supplied to the wafer surface via a flowmeter 5 for monitoring the amount of HMDS which is flowing. Usually, the amount of HMDS which is flowing is monitored using a visual indicator 7 (e.g., a floating ball, represented in FIG. 1 as a triangle) which floats to a predetermined height which corresponds to the amount of gaseous nitrogen which is flowing into the flowmeter 5 together with HMDS.
HMDS passing through the flowmeter 5 is vaporized at a high temperature and then deposited on the wafer surface in an HMDS processor 9. The remaining gaseous HMDS is eliminated via a waste line 15 due to its toxicity to the human body. Subsequent to such treatment, a photosensitive layer is deposited on the HMDS-treated wafer in a spin portion 17.
In the gaseous nitrogen supplying portion 3, gaseous nitrogen flows in thereto via a regulator 21 and a gaseous nitrogen flowmeter 23 in sequence. The gaseous nitrogen then flows to the container 1 via a filter 27 by the operation of a valve 25.
As described above, in the conventional HMDS supplying apparatus, gaseous nitrogen supplied from the gaseous nitrogen supplying portion 3 passes through the flowmeter 5 via the container 1 containing liquid HMDS. In such an apparatus, the flowing of HMDS via the flowmeter 5 can be monitored by visually inspecting the ball 7 of the flowmeter 5, which floats to a height proportional to the amount of HMDS flowing through the flowmeter 5.
Thus, while the photosensitive layer depositing apparatus is operating, if HMDS does not flow or is interrupted due to an error in, the apparatus supplying the HMDS, the HMDS flow cannot be monitored effectively. As a result, the photosensitive layer may be poorly deposited and cause to become separated during the photolithography process. As discussed above, this can cause the production of inferior semiconductor devices. Since there is no device for automatically detecting an abnormality in the HMDS flow in the conventional HMDS supplying apparatus, if a malfunction occurs during the photolithography process, the productivity for semiconductor devices is lowered.